![](http://www.metro-pole.net/x/RER_17.gif)
It is official, the extention of the RER E will be an underground tunnel between Saint Lazare and Nanterre (near la Defense), after this line will use existing track to Mantes la Jolie.
There is three new underground stations planned.
Porte Maillot
Under the roundabound of Porte Maillot this station, connection with the metro line 1 and RER C
La Defense
Under the
CNIT, connection with the RER A, metro line 1, suburban trains and light rail T2.
Nanterre-la Folie
Located in an area under in development.